Actuator element including fat and oil or water repellent

ABSTRACT

A conductive thin film is composed of a polymer gel including carbon nanotubes, an ionic liquid, and a polymer. At least one selected from the group consisting of fat and oil and a water repellent is included in the polymer gel or in a surface of the polymer gel.

CLAIM OF PRIORITY

This application is a continuation of U.S. application Ser. No.13/542,097, filed Jul. 5, 2012, which claims benefit of Japanese PatentApplication No. 2011-149729 filed on Jul. 6, 2011, both of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a conductive thin film, an electrolyticfilm, a layered body of the films, and an actuator element. The actuatorelement herein is an actuator element that is driven through anelectrochemical process such as an electrochemical reaction or thecharge and discharge of an electric double layer.

2. Description of the Related Art

An actuator element that uses a gel of carbon nanotubes and an ionicliquid as a conductive active layer with elasticity has been proposed asan actuator element that can operate in air or vacuum (refer to JapaneseUnexamined Patent Application Publication No. 2005-176428).

General actuator elements have a structure in which an ionic liquid gelserving as an electrolytic layer is sandwiched between electrode layersincluding carbon nanotubes, an ionic liquid, and a polymer. Such anactuator element is excellent in terms of quick deformation, but theamount of deformation is decreased after a voltage is applied for a longtime.

SUMMARY OF THE INVENTION

To further improve the functions of an actuator element, the presentinvention provides an actuator element which provides a large amount ofdeformation and in which the amount of deformation is not significantlychanged even after a voltage is applied for a long time.

As a result of thorough studies, the inventors of the present inventionhave found that, by providing at least one selected from the groupconsisting of fat and oil and a water repellent in a conductive thinfilm and an electrolytic film that constitute an actuator element or atan interface between the conductive thin film and the electrolytic film,a decrease in the amount of deformation (return after deformation) issuppressed and the maximum displacement is increased. They also havefound that, by adjusting the content of an ionic liquid in anelectrolytic film including the ionic liquid and a polymer, a decreasein the amount of deformation (return after deformation) is suppressedand the maximum displacement is increased.

The present invention provides the following conductive thin film,electrolytic film, layered body including the films, and actuatorelement.

According to an aspect of the present invention, a layered body includesat least one conductive thin film composed of a polymer gel includingcarbon nanotubes, an ionic liquid, and a polymer and at least oneelectrolytic film including an ionic liquid and a polymer, theelectrolytic film being stacked on the conductive thin film. At leastone selected from the group consisting of fat and oil and a waterrepellent is included in the polymer gel or in a surface of the polymergel.

The fat and oil may be selected from the group consisting of salad oil,shirashime oil, corn oil, soybean oil, sesame oil, rapeseed oil, riceoil, rice-bran oil, camellia oil, safflower oil, palm kernel oil,coconut oil, cottonseed oil, sunflower oil, perilla oil, olive oil,peanut oil, almond oil, avocado oil, hazelnut oil, walnut oil, grapeseed oil, mustard oil, lettuce oil, fish oil, whale oil, shark oil,cod-liver oil, a glycerol fatty acid ester, a polyglycerol fatty acidester, a sucrose fatty acid ester, an ethylene fatty acid ester, apropylene glycol fatty acid ester, a sorbitan fatty acid ester, apolyoxyethylene fatty acid ester, a polyoxyethylene sorbitan fatty acidester, a polyoxyethylene sorbitol fatty acid ester, a polyoxyethylenelanolin fatty acid ester, a trimethylolpropane fatty acid ester,beeswax, rice wax, hydrogenated fat and oil, a polyglycerol condensed(poly)ricinoleic acid ester, phospholipid, lecithin, egg yolk lecithin,lysolecithin, soybean lecithin, an organic acid monoglyceride, apolyoxyethylene alkyl ether, polyoxyethylene castor oil, sodium stearoyllactate, calcium stearoyl lactate, saponin, quillaia saponin, succinicacid monoglyceride, and succinic acid diglyceride.

The water repellent may be at least one selected from the groupconsisting of fluorine-based oil, fluorosilicone oil, and silicone oil.

The conductive thin film may further include a conductive aid.

The conductive aid may be selected from the group consisting of aconductive polymer, carbon particles, and an inorganic mesoporousmaterial.

According to another aspect of the present invention, a layered bodyincludes at least one conductive thin film composed of a polymer gelincluding carbon nanotubes, an ionic liquid, and a polymer and at leastone electrolytic film including an ionic liquid and a polymer, theelectrolytic film being stacked on the conductive thin film. At leastone selected from the group consisting of fat and oil and a waterrepellent is included in the electrolytic film or in a surface of theelectrolytic film.

According to another aspect of the present invention, a layered bodyincludes at least one conductive thin film composed of a polymer gelincluding carbon nanotubes, an ionic liquid, and a polymer and at leastone electrolytic film including an ionic liquid and a polymer, theelectrolytic film being stacked on the conductive thin film. At leastone selected from the group consisting of fat and oil and a waterrepellent is included in an interface between the conductive thin filmand the electrolytic film.

According to another aspect of the present invention, an actuatorelement includes one of the layered bodies described above.

According to the present invention, an actuator element in which thereturn after deformation is suppressed and the degree of expansion andcontraction and a force to be generated are improved can be provided byusing fat and oil and/or a water repellent or setting the content of anionic liquid in an electrolytic film in a certain range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a displacement measuring system including a laserdisplacement meter that is used in a method for evaluating thedisplacement of an actuator element in Examples of the presentinvention;

FIG. 2A schematically shows an example of an actuator element(three-layer structure) according to an embodiment of the presentinvention;

FIG. 2B schematically shows an example of an actuator element(five-layer structure) according to an embodiment of the presentinvention;

FIG. 3 shows the operating principle of the actuator element accordingto an embodiment of the present invention;

FIG. 4 schematically shows another example of the actuator elementaccording to an embodiment of the present invention;

FIGS. 5A to 5C show that the return after deformation is suppressed andthe amount of deformation is improved by using fat and oil or a waterrepellent; and

FIGS. 6A to 6F show that the return after deformation is suppressed andthe amount of deformation is improved by adjusting the content of anionic liquid in an electrolytic film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, fat and oil and/or a water repellent is usedin at least one of a conductive thin film and an electrolytic film of anactuator element. The conductive thin film used as an electrode layer ofthe actuator element includes carbon nanotubes, a polymer, and an ionicliquid and furthermore may include fat and oil and/or a water repellent.The electrolytic film includes a polymer and an ionic liquid andfurthermore may include fat and oil and/or a water repellent.

Examples of the fat and oil used in the present invention include fattyoils such as salad oil, shirashime oil (refined oil), corn oil, soybeanoil, sesame oil, rapeseed oil, rice oil, rice-bran oil, camellia oil,safflower oil, palm kernel oil, coconut oil, cottonseed oil, sunfloweroil, perilla oil, olive oil, peanut oil, almond oil, avocado oil,hazelnut oil, walnut oil, grape seed oil, mustard oil, lettuce oil, fishoil, whale oil, shark oil, and cod-liver oil; fats which are solid atordinary temperature, such as cocoa butter, palm oil, lard, beef tallow,chicken fat, mutton tallow, horse fat, shortening, butterfat, butter,margarine, ghee, and hydrogenated oil; and lubricating oil, castor oil,grease, cutting oil, glycerol fatty acid esters, polyglycerol fatty acidesters, sucrose fatty acid esters, ethylene fatty acid esters, propyleneglycol fatty acid esters, sorbitan fatty acid esters, polyoxyethylenefatty acid esters, polyoxyethylene sorbitan fatty acid esters,polyoxyethylene sorbitol fatty acid esters, polyoxyethylene lanolinfatty acid esters, trimethylolpropane fatty acid esters, beeswax, ricewax, hydrogenated oils and fats, polyglycerol condensed (poly)ricinoleicacid esters, phospholipids, lecithin, egg yolk lecithin, lysolecithin,soybean lecithin, organic acid monoglycerides, polyoxyethylene alkylethers, polyoxyethylene castor oil, sodium stearoyl lactate, calciumstearoyl lactate, saponin, quillaia saponin, succinic acidmonoglyceride, and succinic acid diglyceride. Fatty oils which areliquid at ordinary temperature are preferably used. Fat and oil which issolid at ordinary temperature can be used after liquefied by heating orafter dissolved in a solvent or fatty oil containing an ionic liquid.

Examples of the water repellent include water-repellent components suchas fluorine-based oils, fluorosilicone oils, silicone oils,fluorine-based urethane resins, silicone resins, and acrylic resins. Tofurther maintain the water repellency, isopropyl alcohol or ethylalcohol may be added to the water-repellent components.

Examples of the fluorine-based oil include perfluoropolyether polymers,chlorotrifluoroethylene polymers, and some of fluorohydrocarboncompounds. Specifically, Demnum S-20 (manufactured by DAIKIN INDUSTRIES,LTD.) and Daifloil #20 (manufactured by DAIKIN INDUSTRIES, LTD.) can beused as the fluorine-based oil.

The fluorosilicone oil has a structure in which polysiloxane has afluoroalkyl group on its side chain or terminal. Specifically, FS-1265(manufactured by Dow Corning Toray Co., Ltd.), X-22-819 (manufactured byShin-Etsu Chemical Co., Ltd.), and FL100 (manufactured by Shin-EtsuChemical Co., Ltd.) can be used as the fluorosilicone oil.

Examples of the silicone oil include dimethyl silicone oils, methylchloride silicone oils, methylphenyl silicone oils, and organo-modifiedsilicone oils. Specifically, PRX413, SF8417, SF8418, BY16-855B, SF8427,and SF8428 (these products are manufactured by Dow Corning Toray Co.,Ltd.); and X-22-161C, KF-857, KP-358, and KP-359 (these products aremanufactured by Shin-Etsu Chemical Co., Ltd.) can be used as thesilicone oil. Oil such as silicone oil preferably has high waterrepellency and relatively low viscosity.

The fats and oils above may be used alone or in combination. The waterrepellents above may be used alone or in combination.

In a preferred embodiment of the present invention, fat and oil and/or awater repellent can be made to be present at an interface between theconductive thin film and the electrolytic film. Specifically, fat andoil and/or a water repellent is applied to a surface of the conductivethin film on the electrolytic film side and/or one surface or bothsurfaces (preferably both surfaces) of the electrolytic film. Theconductive thin film and the electrolytic film are bonded to each otherby compression bonding or the like. In other words, the conductive thinfilm and the electrolytic film are laminated, fabricated by thermaltreating (heat-pressing), etc. Thus, a layer composed of the fat and oiland/or the water repellent can be made to be present at an interfacebetween the conductive thin film and the electrolytic film. The fat andoil and/or the water repellent may be applied to both a surface of theconductive thin film and a surface of the electrolytic film and theobtained two layers may be stacked on top of one another. However, alayer of the fat and oil and/or the water repellent can be sufficientlymade to be present by applying the fat and oil and/or the waterrepellent to only one of the surface of the conductive thin film and thesurface of the electrolytic film.

The layer of the fat and oil and/or the water repellent may be formed onthe entire contact portion between the conductive thin film and theelectrolytic film or may be formed on only part of the contact portion,such as a central portion or a peripheral portion. The layer of the fatand oil and/or the water repellent is believed to restrict the movementof ions. Therefore, for example, the area (the entire contact portion orpart of the contact portion) in which the layer of the fat and oiland/or the water repellent is formed and the thickness of the layer canbe selected in consideration of increases in response speed andgenerated force and suppression of return after deformation. The layerof the fat and oil and/or the water repellent has a thickness of about0.5 to 50 μm and preferably about 1 to 30 μm.

The fat and oil and/or the water repellent may be included in one of orboth of the conductive thin film and the electrolytic film. In thiscase, the amount of the fat and oil and/or the water repellent added toeach of the films is about 0.5% to 20% by mass and preferably about 1%to 10% by mass. If the amount is excessively large, the movement of ionsis restricted and the response speed is decreased. If the amount isexcessively small, no effect is produced.

The fat and oil and/or the water repellent may be dissolved or dispersedin one of or both of the conductive thin film and the electrolytic film.

The ionic liquid used in the present invention is also referred to as anambient temperature molten salt or simply a molten salt. A molten saltis a salt which is in a molten state in a wide temperature rangeincluding ordinary temperature (room temperature), for example, at 0°C., preferably at −20° C., and more preferably at −40° C. The ionicliquid used in the present invention preferably has high ionicconductivity.

In the present invention, various publicly known ionic liquids can beused. Preferably, such ionic liquids are stable and in a liquid state atordinary temperature (room temperature) or a temperature close toordinary temperature. An ionic liquid preferably used in the presentinvention is composed of a cation (preferably an imidazolium ion or aquaternary ammonium ion) represented by one of general formulae (I) to(IV) below and an anion (X⁻).

In the general formulae (I) to (IV) above, R represents a linear orbranched C₁ to C₁₂ alkyl group or a linear or branched alkyl group whichhas an ether linkage and in which the total number of carbon and oxygenatoms is 3 to 12. In the general formula (I), R¹ represents a linear orbranched C₁ to C₄ alkyl group or a hydrogen atom, and R and R¹ arepreferably different from each other. In the general formulae (III) and(IV), x is an integer of 1 to 4.

Examples of the linear or branched C₁ to C₁₂ alkyl group include amethyl group, an ethyl group, an n-propyl group, an isopropyl group, ann-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, apentyl group, a hexyl group, a heptyl group, an octyl group, a nonylgroup, a decyl group, an undecyl group, and a dodecyl group. The numberof carbon atoms is preferably 1 to 8 and more preferably 1 to 6.

Examples of the linear or branched C₁ to C₄ alkyl group include a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a sec-butyl group, and a t-butyl group.

Examples of the linear or branched alkyl group which has an etherlinkage and in which the total number of carbon and oxygen atoms is 3 to12 include CH₂OCH₃ and (CH₂)_(p)(OCH₂CH₂)_(q)OR² (p is an integer of 1to 4, q is an integer of 1 to 4, and R² represents CH₃ or C₂H₅).

Examples of the anion (X⁻) include a tetrafluoroborate ion (BF₄ ⁻),BF₃CF₃ ⁻, BF₃C₂F₅ ⁻, BF₃C₃F₇ ⁻, BF₃C₄F₉ ⁻, a hexafluorophosphate ion(PF₆ ⁻), a bis(trifluoromethanesulfonyl)imidate ion ((CF₃SO₂)₂N⁻), aperchlorate ion (ClO₄ ⁻), a tris(trifluoromethanesulfonyl)methide ion((CF₃SO₂)₃C⁻), a trifluoromethanesulfonate ion (CF₃SO₃ ⁻), a dicyanamideion ((CN)₂N⁻), a trifluoroacetate ion (CF₃COO⁻), an organic carboxylateion, and a halogen ion.

Specifically, the ionic liquid can be composed of a cation such as1-ethyl-3-methylimidazolium ion or [N(CH₃) (CH₃) (C₂H₅)(C₂H₄OC₂H₄OCH₃)]⁺ and an anion such as a halogen ion or atetrafluoroborate ion. Two or more cations and/or anions may be used tofurther decrease the melting point of the ionic liquid.

A combination of a cation and an anion is not limited to the combinationabove, and any ionic liquid having an electrical conductivity of 0.1Sm⁻¹ or more can be used.

The carbon nanotubes used in the present invention are a carbon materialhaving a structure in which a graphene sheet is rolled in a tubularshape. Carbon nanotubes are broadly divided into single-walled carbonnanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) in termsof the number of surrounding walls. Carbon nanotubes are also dividedinto chiral (helical) carbon nanotubes, zigzag carbon nanotubes, andarmchair carbon nanotubes in terms of the structure of a graphene sheet.In the present invention, any type of carbon nanotubes can be used.

A preferred example of carbon nanotubes in practical use is HiPco(manufactured by Unidym) that can be mass produced from carbon monoxide,but is not limited thereto.

Examples of the polymer used in the present invention include copolymersof a perfluorinated olefin and a fluorinated olefin having a hydrogenatom, such as a polyvinylidene fluoride-hexafluoropropylene (PVDF(HFP))copolymer; homopolymers of a fluorinated olefin having a hydrogen atom,such as polyvinylidene fluoride (PVDF); polytetrafluoroethylene (PTFE)and a tetrafluoroethylene-hexafluoropropylene (TFE(HFP)) copolymer;perfluorosulfonic acid (Nafion); poly(meth)acrylates such aspoly-2-hydroxyethyl methacrylate (poly-HEMA) and polymethyl methacrylate(PMMA); polyethylene oxide (PEG); and polyacrylonitrile (PAN).

In a preferred embodiment of the present invention, the conductive thinfilm used as an electrode layer of an actuator element includes carbonnanotubes, an ionic liquid, a polymer, and fat and oil and/or a waterrepellent (in an inside or surface of the thin film).

The amounts of the carbon nanotubes, ionic liquid, and polymer added tothe conductive thin film are 3% to 90% by mass, 5% to 80% by mass, and4% to 70% by mass, respectively. Preferably, the amounts are 16.6% to70% by mass, 15% to 73.4% by mass, and 10% to 68.4% by mass,respectively. More preferably, the amounts are 20% to 50% by mass, 20%to 69% by mass, and 11% to 64% by mass, respectively.

When the fat and oil and/or the water repellent is used in theconductive thin film, the fat and oil and/or the water repellent isadded in an amount of 0.5 to 20 parts by mass and preferably 1 to 10parts by mass relative to 100 parts by mass of the total amount of thecarbon nanotubes, ionic liquid, and polymer.

When the fat and oil and/or the water repellent is used in theelectrolytic film, the fat and oil and/or the water repellent is addedin an amount of 0.1 to 20 parts by mass and preferably 1 to 10 parts bymass relative to 100 parts by mass of the total amount of the ionicliquid and polymer.

The above-described amount of the fat and oil and/or the water repellentadded can also be employed as an amount of fat and oil and/or a waterrepellent used when the fat and oil and/or the water repellent isapplied to form a film at an interface between the conductive thin filmand the electrolytic film.

The electrolytic film needs to include the polymer, but does notnecessarily include the ionic liquid.

When the fat and oil and/or the water repellent is used for an actuatorelement or a layered body including the conductive thin film andelectrolytic film, the amounts of the ionic liquid and polymer added tothe electrolytic film are 0% to 80% by mass and 20% to 100% by mass,respectively. Preferably, the amounts are 0.5% to 60% by mass and 40% to99.5% by mass, respectively. More preferably, the amounts are 1% to 50%by mass and 50% to 99% by mass, respectively.

When the fat and oil and/or the water repellent is not used for anactuator element or a layered body including the conductive thin filmand electrolytic film, the amounts of the ionic liquid and polymer addedto the electrolytic film are 0% to 30% by mass and 70% to 100% by mass,respectively. Preferably, the amounts are 1% to 25% by mass and 75% to99% by mass, respectively. More preferably, the amounts are 2% to 5% bymass and 95% to 98% by mass, respectively.

The conductive thin film used in the present invention may include aconductive aid, in addition to the carbon nanotubes, ionic liquid, andpolymer.

Examples of the conductive aid include conductive polymers; inorganicmesoporous materials; metal oxides such as ruthenium oxide (RuO₂);carbon particles such as carbon black, Ketjenblack, acetylene black,artificial graphite, carbon fiber, furnace black, channel black,lampblack, and thermal black; and gold fine particles.

The conductive aid is added in order to improve the electronicconductivity in an electrode, increase the density of a polymer networkstructure formed of the carbon nanotubes and polymer, and increase aforce to be generated.

Examples of the conductive polymer include polyacetylene, polyaniline,polythiophene, polypyrrole, polyfluorene, polyphenylene, polyphenylenesulfide, poly(1,6-heptadiyne), polybiphenylene (polyparaphenylene),polyparaphenylene sulfide, polyphenylacetylene, poly(2,5-thienylene),polyindole, poly-2,5-diaminoanthraquinone, poly(o-phenylenediamine),poly(quinolinium) salts, poly(isoquinolinium) salts, polypyridine,polyquinoxaline, and polyphenylquinoxaline. These conductive polymersmay have a substituent. Examples of the substituent include a linear orbranched C₁ to C₁₂ alkyl group, a hydroxyl group, a linear or branchedC₁ to C₁₂ alkoxy group, an amino group, a carboxyl group, a sulfonicacid group, a halogen group, a nitro group, a cyano group, a linear orbranched C₁ to C₁₂ alkylsulfonic acid group, and a di(linear or branchedC₁ to C₄ alkyl)amino group.

The inorganic mesoporous material has a structure in whichone-dimensional pores are regularly arranged. The phrase “structure inwhich one-dimensional pores are regularly arranged” means any structurein which one-dimensional pores having a uniform pore size are regularlyarranged. The phrase “regularly arranged” means that pores are alignedin a uniaxial orientation. The phrase “uniform pore size” means that thepore size of each of pores is within a certain range. The pore size canbe suitably set, but is normally 1 to 30 nm and preferably 1.5 to 15 nm.The pore size can be adjusted by changing the type of surfactant.Specific examples of the structure in which one-dimensional pores areregularly arranged include a hexagonal structure, an orthorhombicstructure, and a monoclinic structure.

Such an inorganic mesoporous material can be prepared by using, as amold, a surfactant that can form a regular pore structure.

A desired material can be suitably used as the inorganic mesoporousmaterial. Examples of the inorganic mesoporous material include silica,titania, zirconia, alumina, silica-alumina, silica-titania, tinphosphate, niobium phosphate, aluminum phosphate, titanium phosphate;oxides, nitrides, sulfides, selenides, and tellurides of the foregoingmetal; and composite oxides and composite salts of the foregoing metal.Among them, silicon oxide such as silica is particularly preferred interms of high thermal resistance, high chemical resistance, and goodmechanical properties.

A preferred inorganic mesoporous material is MCM-41. MCM-41 has aregular structure (honeycomb structure) with a pore size of 2.7 nm and aspecific surface area of less than 1000 m²/g, which are approximatelyequivalent to those of carbon nanotubes. By employing MCM-41, the amountof carbon nanotubes added can be reduced, which decreases the cost, andMCM-41 can be made to function as a one-dimensional channel throughwhich an ionic liquid can efficiently move. Although the inventors ofthe present invention do not like to rely on theory, they believe thatan inorganic mesoporous material can be used for efficient adsorption ofcations or as a mold of an electrode.

The conductive thin film used in an electrode layer of an actuatorelement includes carbon nanotubes, an ionic liquid, a polymer, and aconductive aid.

The amounts of the carbon nanotubes, ionic liquid, and polymer added tothe conductive thin film are 3% to 90% by weight, 5% to 80% by weight,and 4% to 70% by weight, respectively. Preferably, the amounts are 16.6%to 70% by weight, 15% to 73.4% by weight, and 10% to 68.4% by weight,respectively. More preferably, the amounts are 20% to 50% by weight, 20%to 69% by weight, and 11% to 64% by weight, respectively. The conductiveaid is added in an amount of 3 to 90 parts by weight, preferably 10 to72.5 parts by weight, and more preferably 15 to 65 parts by weightrelative to 100 parts by weight of the total amount of the carbonnanotubes, ionic liquid, and polymer.

The actuator element according to an embodiment of the present inventionhas, for example, a three-layer structure in which an electrolytic film1 is sandwiched between two conductive thin films (electrode layers) 2including carbon nanotubes, an ionic liquid, and a polymer (andoptionally fat and oil and/or a water repellent) (refer to FIG. 2A). Theelectrolytic film 1 may include fat and oil and/or a water repellent. Inthis case, the conductive thin film 2 does not necessarily include fatand oil and/or a water repellent. The fat and oil and/or the waterrepellent may be present at interfaces between the electrolytic film 1and the two conductive thin films (electrode layers) 2.

To increase the surface conductivity of electrodes, the actuator elementaccording to an embodiment of the present invention may have afive-layer structure in which a conductive layer 3 is further formed oneach of the outer sides of the two electrode layers 2 (refer to FIG.2B).

The actuator element can be obtained by stacking a conductive thin filmon the surface of an electrolytic film. Specifically, an electrodelayer-forming gel solution prepared by dispersing carbon nanotubes, anionic liquid, and a polymer (and optionally fat and oil and/or a waterrepellent) in a solvent and an electrolytic film-forming gel solutioncomposed of an ionic liquid and a polymer (and optionally fat and oiland/or a water repellent) are each cast and dried, and the formed filmsare alternately stacked on top of one another. Alternatively, aconductive thin film formed by casting and drying the electrodelayer-forming gel solution is stacked, through thermocompressionbonding, on an electrolytic film formed by casting and drying theelectrolytic film-forming gel solution.

In the actuator element having the three-layer structure shown in FIG.2A, the fat and oil and/or the water repellent can be made to be presentat interfaces between the electrolytic film and the two conductive thinfilms in the following manner. That is, fat and oil and/or a waterrepellent may be applied to one of the main surfaces of each of the twoconductive thin films and/or may be applied to both the surfaces of theelectrolytic film. Layers of the fat and oil and/or the water repellentmay be formed on both the surfaces of the electrolytic film through asingle step by immersing the electrolytic film in a solution of the fatand oil and/or the water repellent and drying it.

In the present invention, when the conductive thin film including carbonnanotubes, an ionic liquid, and a polymer (and optionally fat and oiland/or a water repellent) is formed, it is important to uniformly mixthe components. A solvent is preferably used to prepare a dispersionliquid containing the components uniformly mixed therein. For example, amixed solvent of a hydrophobic solvent and a hydrophilic solvent isparticularly preferably used.

Examples of the hydrophilic solvent include carbonates such as ethylenecarbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate,methylethyl carbonate, and butylene carbonate; ethers such astetrahydrofuran; acetone; lower alcohols having 1 to 3 carbon atoms,such as methanol and ethanol; and acetonitrile. Examples of thehydrophobic solvent include ketones having 5 to 10 carbon atoms, such as4-methylpentan-2-one; halogenated hydrocarbons such as chloroform andmethylene chloride; aromatic hydrocarbons such as toluene, benzene, andxylene; aliphatic and alicyclic hydrocarbons such as hexane andcyclohexane; and N,N-dimethylacetamide and N-methyl-2-pyrrolidone.

A dispersion liquid used to produce the conductive thin film accordingto an embodiment of the present invention may be prepared by kneading anionic liquid and carbon nanotubes (and optionally fat and oil and/or awater repellent) to form a gel and then adding a polymer and a solvent(e.g., a mixed solvent of a hydrophilic solvent and a hydrophobicsolvent when the ionic liquid has hydrophilicity and a hydrophobicsolvent when the ionic liquid has hydrophobicity) to the gel.Alternatively, the dispersion liquid may be prepared by mixing carbonnanotubes, an ionic liquid, and a polymer and optionally a solvent(e.g., a mixed solvent of a hydrophilic solvent and a hydrophobicsolvent when the ionic liquid has hydrophilicity and a hydrophobicsolvent when the ionic liquid has hydrophobicity) and fat and oil and/ora water repellent with each other without forming a gel. In this case,it is also effective to disperse the components using ultrasonic waves.

In the case where the dispersion liquid is prepared through theformation of a gel, the mass ratio of the hydrophilic solvent to thehydrophobic in the mixed solvent is preferably 20:1 to 1:10 and morepreferably 2:1 to 1:5.

In the case where the dispersion liquid is prepared without forming agel, the ratio of the hydrophilic solvent to the hydrophobic solvent ispreferably 1/100 to 20/100 and more preferably 3/100 to 15/100. A singlesolvent can also be used and, in this case, N,N-dimethylacetamide orN-methyl-2-pyrrolidone is preferably used.

The conductive thin film is composed of a polymer gel including carbonnanotubes, an ionic liquid, and a polymer (and optionally fat and oiland/or a water repellent).

The mixing ratio (by mass) of the carbon nanotubes and ionic liquidrelative to the polymer in the conductive thin film is preferably 1:2 to4:1 and more preferably 1:1 to 3:1. Herein, a mixed solvent of ahydrophilic solvent and a hydrophobic solvent is employed. A dispersionliquid for forming conductive thin films can also be prepared by mixingcarbon nanotubes and an ionic liquid to form a gel in advance and thenadding a polymer and a solvent (preferably a hydrophobic solvent) to thegel. In this case, the mixing ratio of the carbon nanotubes and ionicliquid relative to the polymer is preferably 1:1 to 3:1. The conductivethin film may contain a small amount of the solvent (hydrophobic solventand hydrophilic solvent), but a solvent that can be removed undertypical drying conditions is preferably removed in advance as much aspossible.

A gel composition used to form the ion conductive layer (electrolyticfilm) includes a polymer and an ionic liquid that is an optionalcomponent (and optionally fat and oil and/or a water repellent). In theion conductive layer, the mixing ratio (by mass) of a hydrophilic ionicliquid to a polymer in the gel composition is preferably 1:4 to 4:1 andmore preferably 1:2 to 2:1. Also in this case, a solvent prepared bymixing a hydrophilic solvent and a hydrophobic solvent at a desiredratio is preferably used.

The ion conductive layer functioning as a separator that separates twoor more conductive thin films can be formed by dissolving a polymer in asolvent and performing a typical process such as coating, printing,extrusion molding, casting, or injection molding. The ion conductivelayer may be formed of substantially only a polymer or may be formed ofa polymer to which an ionic liquid has been added.

The polymers used for the conductive thin film and ion conductive layermay be the same as or different from each other, but the polymers arepreferably the same as each other or the characteristics thereof arepreferably similar to each other in terms of the adhesion between theconductive thin film and the ion conductive layer.

The thickness of the electrolytic film is preferably 5 to 200 μm andmore preferably 10 to 100 μm. The thickness of the conductive thin filmis preferably 10 to 500 μm and more preferably 50 to 300 μm. Theelectrolytic film and conductive thin film can also be formed by spincoating, printing, spraying, extrusion molding, injection molding, orthe like.

In the thus-obtained actuator element, when a direct-current voltage of0.5 to 4 V is applied between electrodes (which are connected to theconductive thin films), a displacement that is about 0.05 to 1 times thelength of the actuator element can be obtained within several seconds.The actuator element can operate in a flexible manner in air or vacuum.

FIG. 3 shows the operating principle of the actuator element. When apotential difference is applied between the two conductive thin films 2formed on the two surfaces of the electrolytic film 1 so as to beinsulated from each other, an electric double layer is formed at aninterface between a carbon nanotube phase and an ionic liquid phase ineach of the two conductive thin films 2. As a result, the two conductivethin films 2 expand and contract due to the interfacial stress caused bythe electric double layer. As shown in FIG. 3, the actuator elementbends toward the positive electrode side. This may be because carbonnanotubes significantly expand on the negative electrode side due toquantum chemical effects, and the ionic radius of cations 4 in an ionicliquid often used at present is large and the conductive thin film 2 onthe negative electrode side expands more than that on the positiveelectrode side due to its steric effect. In FIG. 3, the referencenumeral 4 indicates a cation in the ionic liquid and the referencenumeral 5 indicates an anion in the ionic liquid.

According to the actuator element that can be obtained by the methodabove, the effective area of a gel at an interface between the carbonnanotubes and the ionic liquid is significantly increased and thus theimpedance at the electric double layer at the interface is decreased.Consequently, the electrically-expanding-and-contracting effects of thecarbon nanotubes can be effectively utilized. From a mechanical point ofview, the adhesion between the conductive thin film and the electrolyticfilm at the interface is improved and thus the actuator element has highdurability. As a result, an actuator element having quick response and alarge amount of displacement in air or vacuum and having high durabilitycan be obtained. In addition, such an actuator element has a simplestructure, is easily downsized, and can be operated with low powerconsumption. Furthermore, by adding a conductive additive to the carbonnanotubes, the conductivity and filling factor (packing density) of anelectrode layer are improved and a force is efficiently generatedcompared with typical actuator elements of the same type.

The actuator element according to an embodiment of the present inventionhas high durability in air or vacuum and operates at low voltage in aflexible manner. Therefore, the actuator element can be suitably usedfor actuators of robots that work for human beings and thus need to havehigh safety (e.g., actuators of personal robots such as house robots,pet robots, and amusement robots); actuators of robots that operate inspecial environments, for example, in a space environment, in a vacuumchamber, and in a rescue situation; actuators of medical and welfarerobots used for operation devices, muscle suits, and bedsore prevention;and actuators of brakes and micromachines.

In particular, to produce products with high purity in a vacuumenvironment or an ultra-clean environment, a demand for actuators usedfor the conveyance and positioning of samples has been growing. Theactuator element according to an embodiment of the present inventionthat uses a nonvolatile ionic liquid can be effectively used foractuators that cause no contamination and operate in a vacuumenvironment.

At least two conductive thin films need to be formed on the surfaces ofthe electrolytic film. As shown in FIG. 4, a large number of conductivethin films 2 can be disposed on the surfaces of a planar electrolyticfilm 1 to achieve a complicated motion. Such an actuator element canrealize the conveyance that uses peristaltic movement and can provide amicromanipulator. The shape of the actuator element according to anembodiment of the present invention is not limited to a planar shape,and an actuator element having any shape can be easily produced. Forexample, an actuator element may include a rod-shaped electrolytic filmhaving a diameter of about 1 mm and four conductive thin films formedaround the electrolytic film. By using the actuator element, an actuatorthat can be inserted into a thin tube can be realized.

EXAMPLES

The present invention will now be described in detail based on Examples,but is obviously not limited to Examples.

In Examples, the displacement of an actuator element was evaluated asfollows.

That is, an actuator element was cut into rectangles having a size of 1mm×10 mm or 2 mm×10 mm, and a displacement, at a position 5 mm from oneend, caused when a voltage was applied was measured with a laserdisplacement meter shown in FIG. 1.

The ionic liquid (IL) used in Examples 1 to 7 and Comparative Example 1was ethylmethylimidazolium tetrafluoroborate (EMIBF₄).

The carbon nanotubes used in Examples 1 to 7 and Comparative Example 1were purified-grade single-walled carbon nanotubes (hereinafter alsoreferred to as “SWCNTs”) (“HiPco” manufactured by Unidym).

The polymer used in Examples 1 to 7 and Comparative Example 1 was apolyvinylidene fluoride-hexafluoropropylene (PVDF(HFP)) copolymer(product name: kynar 2801) represented by formula (III) below.

The solvent used in Examples 1 to 7 and Comparative Example 1 wasN,N-dimethylacetamide (DMAC).

The fat and oil used in Examples 1 to 7 was salad oil (manufactured byThe Nisshin OilliO Group, Ltd.).

The water repellent used in Examples 1 to 7 was Scotchgard (productname) manufactured by Sumitomo 3M Limited.

Preparation Example 1 Preparation of Dispersion Liquid for FormingConductive Thin Films

The carbon nanotubes (SWCNTs), the ionic liquid (IL), and the polymer(powdery PVDF(HFP)) were dispersed in the DMAC solvent, stirred with amagnetic stirrer, and then dispersed using ultrasonic waves to prepare adispersion liquid for forming conductive thin films.

[Preparation of Solution for Forming Electrolytic Films]

The ionic liquid (IL) and the polymer (powdery PVDF(HFP)) were dissolvedin a solvent in a manner similar to that of the dispersion liquid forforming conductive thin films to prepare a solution for formingelectrolytic films. The solvent used herein was a mixed solvent of4-methylpentan-2-one and propylene carbonate.

[Production of Actuator Element]

The dispersion liquid and solution prepared as described above wereseparately cast, dried at room temperature for about twenty-for hours,and then vacuum-dried to form a conductive thin film and an electrolyticfilm, respectively. The fat and oil or the water repellent was appliedto the surfaces of two conductive thin films to form fat and oil layersor water repellent layers. The electrolytic film was sandwiched betweenthe two conductive thin films so that the fat and oil layers or waterrepellent layers of the two conductive thin films face the electrolyticfilm. Subsequently, thermocompression bonding (fabrication byheat-pressing) was performed to produce an actuator element having athree-layer structure.

[Evaluation Method of Actuator Element]

The displacement response of the produced actuator element was evaluatedwith the system shown in FIG. 1. The actuator element was cut intorectangles having a width of 2 mm and a length of 10 mm. A portion 3 mmfrom one end of each of the rectangles was gripped with a holder alsofunctioning as an electrode. A displacement, at a position 5 mm from thegripped end, caused when a voltage was applied in air was measured withthe laser displacement meter. The frequency of the voltage was changedfrom 5 mHz to 200 Hz. The long-term durability of the actuator elementwas evaluated by continuously applying a constant voltage of +2.0 V.

Examples 1 and 2 Coating with Fat and Oil or Water Repellent

A film-like actuator element having a five-layer structure of conductivethin film (electrode)-(fat and oil layer or water repellentlayer)-electrolytic film-(fat and oil layer or water repellentlayer)-conductive thin film (electrode) was produced using the carbonnanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer (PVDF(HFP), kynar2801) at the ratios shown below. The fat and oil (weight: 0.12 mg)(Example 1) or the water repellent (weight: 1.0 mg) (Example 2) wasapplied to one of the main surfaces of each of the two conductive thinfilms, and compression bonding (heat-pressing) was performed so that thefat and oil layer or the water repellent layer faced the electrolyticfilm.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=50.2 mg/80.1mg/120.2 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=20.04wt %/31.98 wt %/47.98 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.3 mg/200.1 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=50.02 wt%/49.98 wt %

Example 3 The Case where the Conductive Thin Film has the SameComposition as that of the Reference Film in Examples 1 and 2 and theContent of the Ionic Liquid in the Electrolytic Film is 0 wt %

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Example 3 using thecarbon nanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer(PVDF(HFP), kynar 2801) at the ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=50.1 mg/80.1mg/120.5 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=19.98wt %/31.95 wt %/48.07 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.1 mg/0.0 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=100.00 wt%/0.00 wt %

Example 4 The Case where the Conductive Thin Film has the SameComposition as that of the Reference Film in Examples 1 and 2 and theContent of the Ionic Liquid in the Electrolytic Film is 1 wt %

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Example 4 using thecarbon nanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer(PVDF(HFP), kynar 2801) at the ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=25.26mg/40.4 mg/60.2 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=20.07wt %/32.10 wt %/47.83 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.3 mg/2.1 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=98.96 wt %/1.04wt %

Example 5 The Case where the Conductive Thin Film has the SameComposition as that of the Reference Film in Examples 1 and 2 and theContent of the Ionic Liquid in the Electrolytic Film is 2 wt %

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Example 5 using thecarbon nanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer(PVDF(HFP), kynar 2801) at the ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=50.1 mg/80.1mg/120.4 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=19.99wt %/31.96 wt %/48.04 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.1 mg/4.1 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=97.99 wt %/2.01wt %

Example 6 The Case where the Conductive Thin Film has the SameComposition as that of the Reference Film in Examples 1 and 2 and theContent of the Ionic Liquid in the Electrolytic Film is 5 wt %

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Example 6 using thecarbon nanotubes

(SWCNTs), ionic liquid (EMIBF₄), and polymer (PVDF(HFP), kynar 2801) atthe ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=50.1 mg/80.1mg/120.4 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=19.99wt %/31.96 wt %/48.04 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.4 mg/10.8 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=94.89 wt %/5.11wt %

Example 7 The Case where the Conductive Thin Film has the SameComposition as that of the Reference Film in Examples 1 and 2 and theContent of the Ionic Liquid in the Electrolytic Film is 10 wt %

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Example 7 using thecarbon nanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer(PVDF(HFP), kynar 2801) at the ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=25.26mg/40.4 mg/60.2 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=20.07wt %/32.10 wt %/47.83 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.3 mg/22.3 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=89.98 wt%/10.02 wt %

Comparative Example 1

A film-like actuator element having a three-layer structure ofconductive thin film (electrode)-electrolytic film-conductive thin film(electrode) was produced as an actuator element of Comparative Example 1using the carbon nanotubes (SWCNTs), ionic liquid (EMIBF₄), and polymer(PVDF(HFP), kynar 2801) at the ratios shown below.

Composition of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=50.1 mg/80.1mg/120.5 mgComposition ratio of conductive thin film: SWCNT/PVDF(HFP)/EMIBF₄=19.98wt %/31.95 wt %/48.07 wt %Composition of electrolytic film: PVDF(HFP)/EMIBF₄=200.2 mg/200.3 mgComposition ratio of electrolytic film: PVDF(HFP)/EMIBF₄=49.99 wt%/50.01 wt %

Test Example 1

The response of each of the actuator elements produced in Examples 1 to7 and Comparative Example 1 when a voltage was applied was evaluated bythe above-described method for evaluating an actuator element. FIGS. 5Ato 5C and 6A to 6F show the results.

As is clear from the results shown in FIGS. 5A to 5C and 6A to 6F, thereturn after deformation was suppressed in the actuator elementaccording to an embodiment of the present invention in which a fat andoil layer or a water repellent layer was formed and in the actuatorelement according to an embodiment of the present invention in which thecontent of an ionic liquid in the electrolytic film was 0% to 10% bymass. In the case where the content of the ionic liquid in theelectrolytic film was adjusted, when the content of the ionic liquid was2% to 5% by mass, the return after deformation was significantlysuppressed. In addition, the maximum displacement increased two to sixtimes.

What is claimed is:
 1. A layered body comprising: at least oneconductive thin film composed of a polymer gel including carbonnanotubes, an ionic liquid, and a polymer; and at least one electrolyticfilm including an ionic liquid and a polymer, the electrolytic filmbeing stacked on the conductive thin film, wherein the ionic liquid inthe electrolytic film is 0% to 10% by mass.
 2. The layered bodyaccording to claim 1, wherein the ionic liquid in the electrolytic filmis 2% to 5% by mass.
 3. The layered body according to claim 1, whereinthe ionic liquid included in the conductive thin film or theelectrolytic film is selected from the group consisting of an ionicliquid composed of a cation represented by one of general formulae (I)to (IV) below and an anion (X⁻),

wherein R represents a linear or branched C₁ to C₁₂ alkyl group or alinear or branched alkyl group which has an ether linkage and in whichthe total number of carbon and oxygen atoms is 3 to 12, R¹ represents alinear or branched C₁ to C₄ alkyl group or a hydrogen atom, and R and R¹are preferably different from each other, and x is an integer of 1 to 4.4. The layered body according to claim 3, wherein the ionic liquid isethylmethylimidazolium tetrafluoroborate (EMIBF₄).
 5. The layered bodyaccording to claim 1 wherein the polymer is one selected from the groupconsisting of copolymers of a perfluorinated olefin and a fluorinatedolefin; homopolymers of a fluorinated olefin having a hydrogen atom;polytetrafluoroethylene (PTFE) and atetrafluoroethylene-hexafluoropropylene (TFE(HFP)) copolymer;perfluorosulfonic acid (Nafion); poly(meth)acrylates such aspoly-2-hydroxyethyl methacrylate (poly-HEMA) and polymethyl methacrylate(PMMA); polyethylene oxide (PEG); and polyacrylonitrile (PAN).
 6. Thelayered body according to claim 5 wherein the polymer is apolyvinylidene fluoride-hexafluoropropylene (PVDF(HFP)) copolymer. 7.The layered body according to claim 1, wherein the conductive thin filmfurther includes a conductive aid.
 8. The layered body according toclaim 7, wherein the conductive aid is selected from the groupconsisting of a conductive polymer, carbon particles, and an inorganicmesoporous material.
 9. An actuator element comprising the layered bodyaccording to claim
 1. 10. An actuator element comprising the layeredbody accoding to claim
 2. 11. An actuator element comprising the layeredbody according to claim
 3. 12. An actuator element comprising thelayered body according to claim
 4. 13. An actuator element comprisingthe layered body according to claim
 5. 14. An actuator elementcomprising the layered body according to claim
 6. 15. An actuatorelement comprising the layered body according to claim
 7. 16. Anactuator element comprising the layered body according to claim 8.